This invention relates to improvements in apparatus for intermittently compressing a patient's leg muscles during surgery or any other periods of muscular inactivity or paralysis in order to accelerate venous blood flow and thereby prevent blood clot formation in the lower extremities and pelvis. More specifically the apparatus is of the type wherein individual pneumatic leggings are provided for fitting around the patient's lower leg and wherein a pneumatic control circuit is provided for automatically regulating the timing, rate of pressurization and maximum pressure of periodic pneumatic pulses delivered alternately to each legging.
Persons undergoing surgery and extended post-operative recovery or prolonged bed rest and inactivity for any reason have in the past been particularly susceptible to a condition known as "deep vein thrombosis" which is a clotting of venous blood in the lower extremities and pelvis. The clotting occurs because of the absence of sufficient muscular activity in the lower legs required to pump the venous blood, and can be life-threatening if a blood clot migrates to the heart and interferes with pulmonary blood circulation. Statistics indicate that deep vein thrombosis occurs to some degree either during or shortly after surgical procedures in approximately 30% of all surgical patients.
Because of the high incidence and potential severity of the condition, several means of thrombosis prevention have been devised in the past. Most notable among these is the provision of pneumatic leggings or boots adapted to fit around the calf and foot of a patient's legs, such leggings being connected to pump apparatus which sends alternate intermittent pulses to each of the leggings to periodically compress and release the calf muscles and thereby accelerate blood flow. No appreciable venous backflow results from such intermittent compression because a series of one-way valves in the venous system permits the blood to move only in an upward direction. Although such apparatus has proven to be effective in the prevention of deep vein thrombosis, it has also suffered from several disadvantages. One serious deficiency has been the reliance of such apparatus on electrical power for pneumatic pumping and timing cycle control, causing a serious fire or explosion hazard when such electrical components are utilized in a surgical or post-operative environment where highly inflammable substances such as anesthesias and oxygen abound. Another disadvantage of prior apparatus is that they provide sufficient adjustability of the pressurization process, such as regulation for each leg of the rate of pressure build-up, the duration of the duty cycle and the maximum pneumatic pressure applied. Consequently the prior apparatus are not sufficiently versatile to be used on a patient whose legs, for example, may be especially tender or sore requiring lower pressure levels, nor is such apparatus adapted to permit the gradual increasing of pressure levels so that the patient may, without experiencing pain, gradually adapt himself to a higher pressure level. Because of the lack of adjustability such prior apparatus are also not adaptable for the treatment of certain conditions where a lower pressure range than that normally desired for the treatment of deep vein thrombosis would be advantageous, such as in the treatment of "venous insufficiency related stasis ulcer". Finally, pneumatic leggings used in the past have been constructed so as to compress most or all of the foot as well as the muscles of the lower leg, a feature which not only provides no particular advantage but tends to limit circulation in the foot and thus may be harmful.
Accordingly there presently exists a need for an improved alternating leg compression system which operates entirely without electricity, thereby eliminating all fire or explosion hazard, and is independently adjustable for each leg with respect to compression levels and the rate of pressure application so that it is adaptable for use with patients having widely varying leg conditions.